Technical Field
The present disclosure relates to a rolled copper foil obtained by rolling a round wire rod comprising one of copper and a copper alloy, and a method of manufacturing the same, as well as a flexible flat cable and a method of manufacturing the same, and particularly relates to a rolled copper foil used for flexible flat cables or the like subjected to repeated bending motions in automotive components and a method of manufacturing the same.
Background Art
Existing flexible flat cables (FFCs) are used for various applications owing to their high degree of freedom in the configuration of installation to electronic devices resulting from features such as a small thickness and an excellent flexibility. For example, they are widely used in applications such as a steering roll connector (SRC), which is a component of an air bag system in automobiles, a foldable section of foldable cell-phones, a movable part of digital cameras, printer heads, or the like, and wirings of a movable part of disc associated devices including HDDs (Hard Disk Drives), DVD (Digital Versatile Disc) drives, Blu-ray Disc drives, and CD (Compact Disc) drives. A rolled copper foil is generally used for a conductor portion of such flexible flat cables.
As an existing rolled copper foil, for example, a rolled copper foil has been disclosed which has a cube texture for which:I/I(0)>20,where I is an integral strength of the (200) plane obtained by X-ray diffraction of a copper foil, and I(0) is an integral strength of the (200) plane obtained by X-ray diffraction of fine powder copper (Japanese Laid-Open Patent Publication No. 2006-326684). It is disclosed that, with this technique, life expectancy can be made longer by using a copper foil having a texture with an excellent flex resistance, and that downsizing and improvement in performance of a flexible printed circuit board (FPC) can be achieved.
As another existing rolled copper foil, a rolled copper foil is disclosed that is manufactured by rolling a round wire rod and for which a crystal average particle diameter with respect to the film thickness is specified (Japanese Patent No. 5342712). According to this technique, a flex resistance is improved by refining crystals in an outermost surface where a break due to fatigue starts.
However, with the technique described in Japanese Laid-Open Patent Publication No. 2006-326684, the copper foil is manufactured by rolling a plate material, and thus when manufacturing a FFC using the copper foil, it is required to perform a slitting process on the copper foil that gives rise to an increase in costs. Further, despite an increasing need for a FFC with a narrower width, it was difficult to sufficiently narrow the width of a copper foil with a method using a slitting process. Also, Japanese Laid-Open Patent Publication No. 2006-326684 does not disclose a technique for manufacturing a copper foil from a round wire.
On the other hand, with a technique of Japanese Patent No. 5342712, it is disclosed that a copper foil is manufactured by rolling a round wire and has a high flex resistance, but texture control is not performed, and recently, there is a need for further improvement in properties to meet the requirements for a high flex resistance required for the aforementioned SRC, for example.
The present disclosure is related to providing a rolled copper foil and a flexible flat cable that have an improved flex resistance and that are capable of achieving an ease of processing and a reduced cost, even when manufacturing a copper foil having a narrow width, as well as methods of manufacturing the same.